Multi-leaf collimator, particle beam therapy system, and treatment planning apparatus

ABSTRACT

There are provided a leaf row in which a plurality of leaf plates are arranged in the thickness direction of the row in such a way that the respective one end faces of the leaf plates are trued up and a leaf plate drive mechanism that drives each of the plurality of leaf plates in such a way that the one end face approaches or departs from a beam axis. In each of the leaf plates, a facing side facing a leaf plate that is adjacent to that leaf plate in the thickness direction is formed of a plane including a first axis on the beam axis; the leaf plate drive mechanism drives the leaf plate along a circumferential orbit around the second axis, on the beam axis, that is perpendicular to the beam axis and the first axis.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/263,594, filed on Apr. 28, 2014, which is a continuation of U.S.application Ser. No. 13/696,931, filed on Nov. 8, 2012, which claimspriority from International Application No. PCT/JP2010/063874, filed onAug. 17, 2010, the contents of which are herein incorporated in theirentirety by reference.

TECHNICAL FIELD

The present invention relates to a multi-leaf collimator that isutilized in order to form an irradiation field in a particle beamtherapy system utilizing a charged particle beam, relates to a particlebeam therapy system utilizing the multi-leaf collimator, and relates toa treatment planning apparatus for determining the operation conditionof the particle beam therapy system.

BACKGROUND ART

In the particle beam therapy, therapy is implemented by irradiating acharged particle beam onto a diseased site, which is a therapy subject,so as to kill tissues of the diseased site; in order to deliver asufficient dose to the tissues of the diseased site without causingdamage to the peripheral tissues thereof, there is required a particlebeam therapy system that can appropriately control an irradiation doseand irradiation coverage (referred to as an irradiation field,hereinafter). In a so-called broad-irradiation-type particle beamtherapy system, among particle beam therapy systems, that utilizes anirradiation nozzle provided with a scanning electromagnet such as awobbler electromagnet, the irradiation nozzle enlarges the irradiationfield and a multi-leaf collimator that changes a penetration shape isdisposed in the enlarged irradiation field, so that an irradiation fieldcorresponding to the shape of a diseased site is formed.

A multi-leaf collimator, in which two leaf lines formed of leaf plateslaminated in the thickness direction are arranged in such a way as toface each other and the leaf plates are driven in a direction in whichthey approach each other or in a direction in which they are separatedfrom each other, forms a predetermined penetration shape. Accordingly,by controlling the respective physical positions of the leaf plates, anirradiation field can readily be formed. However, in the case of alinear-driven leaf plate, in the contour portion that is away from thecenter of the irradiation field, a so-called penumbra is caused in whicha charged particle beam having an angle toward the spreading directionhits part of the end face of the leaf plate and hence the dose of thecharged particle beam is continuously attenuated. Thus, a so-calledcone-shaped multi-leaf collimator has been proposed (e.g., refer toPatent Document 1 or 2) in which the spread of a beam is taken intoconsideration and leaves formed in a shape obtained through division atthe side surface of an arc or a cone are driven on a circular orbit.

PRIOR ART REFERENCE Patent Document

[Patent Document 1] Japanese Patent Application Laid-Open No. S60-063500(top right of Page 2, down right of Page 2 to top left of Page 3, andFIGS. 2 and 4)

[Patent Document 2] Japanese Patent Application Laid-Open No. S63-225199(down right of Page 3 to top right of Page 4, down left to down right ofPage 7, FIGS. 1 through 3, and FIGS. 12 and 13)

[Patent Document 3] Japanese Patent Application Laid-Open No. 10-255707(Paragraphs 0009 through 0020, and FIGS. 1 and 5)

[Patent Document 4] Japanese Patent Application Laid-Open No.2006-166947 (paragraphs 0015 to 0016, and FIG. 1)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, in the case of the foregoing cone-shaped multi-leaf collimator,it is assumed that a beam spreads from a point light source.Alternatively, even in the case where it is assumed that the lightsource is a volume light source, it is not taken into consideration thatthe spreading manner differs depending on the direction. On the otherhand, in order to enlarge an irradiation field in a particle beamtherapy system that utilizes a charged particle beam, there is requiredan electromagnet for scanning a thin beam supplied from the accelerator,as described in Patent Documents 3 and 4. On top of that, there arerequired respective electromagnets such as an X-direction electromagnetand a Y-direction electromagnet for two directions in a planeperpendicular to the beam axis; thus, the spread starting point in the Xdirection and the spread starting point in the Y direction differ fromeach other. Accordingly, there has been a problem that even when theforegoing multi-leaf collimator is applied to a particle beam therapysystem, the beam spreading manner and the penetration shape of themulti-leaf collimator do not coincide with each other and hence apenumbra remains.

The present invention has been implemented in order to solve theforegoing problems; the objective thereof is to obtain a multi-leafcollimator and a particle beam therapy system in which a high-contrastirradiation field can be formed without undergoing the effect of apenumbra.

Means for Solving the Problems

A multi-leaf collimator according to the present invention is disposedin a particle beam that is irradiated so as to enlarge an irradiationfield of that, in order to form the irradiation field so as to beconformed to an irradiation subject; the multi-leaf collimator ischaracterized in that there are provided a leaf row in which a pluralityof leaf plates are arranged in the thickness direction thereof in such away that the respective one end faces of the leaf plates are trued upand a leaf plate drive mechanism that drives each of the plurality ofleaf plates in such a way that the one end face approaches or departsfrom a beam axis of the particle beam, in that in each of the leafplates, a facing side facing a leaf plate that is adjacent to that leafplate in the thickness direction is formed of a plane including a firstaxis that is perpendicular to the beam axis and is set at a firstposition on the beam axis, and in that the leaf plate drive mechanismdrives the leaf plate along a circumferential orbit around a second axisthat is perpendicular to the beam axis and the first axis and is set ata second position on the beam axis.

A particle beam therapy system according to the present invention ischaracterized by including an irradiation nozzle that scans a particlebeam supplied from an accelerator, by use of two electromagnets whosescanning directions are different from each other, and that irradiatesthe particle beam in such a way as to enlarge an irradiation field andthe multi-leaf collimator, disposed in a particle beam irradiated fromthe irradiation nozzle, and characterized in that the multi-leafcollimator is disposed in such a way that the first axis coincides withthe scanning axis of one of the two electromagnets and the second axiscoincides with the scanning axis of the other one of the twoelectromagnets.

A particle beam therapy system according to the present invention ischaracterized by including a three-dimensional data generation unit forgenerating three-dimensional data from image data on an irradiationsubject, an irradiation condition setting unit that sets an irradiationcondition, based on the generated three-dimensional data, and a controldata generation unit that generates control data for controlling leafdriving for the multi-leaf collimator in the foregoing particle beamtherapy system, based on the set irradiation condition, andcharacterized in that the three-dimensional data generation unitgenerates the three-dimensional data by utilizing at least a beamdeflection angle with respect to the first axis and a beam deflectionangle with respect to the second axis.

Advantage of the Invention

In a multi-leaf collimator, a particle beam therapy system, and atreatment planning apparatus according to the present invention, thedirections of the faces of leaf plates that configure a contour at atime when the multi-leaf collimator forms a penetration shape coincidewith the directions of a particle beam spreading and passing through thevicinity of the faces; thus, a high-contrast irradiation field can beformed without undergoing the effect of a penumbra.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining the configuration of an irradiationsystem, of a particle beam therapy system, that is provided with amulti-leaf collimator according to Embodiment 1 of the presentinvention;

FIG. 2( a) and FIG. 2( b) depict views for explaining the configurationof an irradiation system, of a particle beam therapy system, that isprovided with a multi-leaf collimator according to Embodiment 1 of thepresent invention, when the irradiation system is viewed from twodirections that are perpendicular to each other with respect to thecenter of a beam;

FIG. 3( a), FIG. 3( b) and FIG. 3( c) depict views for explaining thebeam-bundle state of a charged particle beam in an irradiation system ofa particle beam therapy system according to Embodiment 1 of the presentinvention;

FIG. 4( a), FIG. 4( b), FIG. 4( c) and FIG. 4( d) depict views forexplaining the configurations of a multi-leaf collimator and a leafplate according to Embodiment 1 of the present invention, when theleaves are all closed;

FIG. 5( a), FIG. 5( b), FIG. 5( c) and FIG. 5( d) depict views forexplaining the configurations of a multi-leaf collimator and a leafplate according to Embodiment 1 of the present invention, when anirradiation field having a predetermined shape is formed;

FIG. 6 is a chart representing an example of beam scanning locus in aparticle beam therapy system according to Embodiment 2 of the presentinvention;

FIG. 7 is a chart representing another example of beam scanning locus ina particle beam therapy system according to Embodiment 2 of the presentinvention;

FIG. 8 is a view for explaining the configurations of a particle beamtherapy system and a multi-leaf collimator according to Embodiment 5 ofthe present invention;

FIG. 9 is a diagram for explaining the flow of medical practice; and

FIG. 10 is a block diagram for explaining the configuration of atreatment planning apparatus according to Embodiment 6 of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

The configurations of a multi-leaf collimator and a particle beamtherapy system according to Embodiment 1 of the present invention willbe explained below. FIGS. 1 through 5 are to explain the configurationsof a multi-leaf collimator and a particle beam therapy system accordingto Embodiment 1 of the present invention. FIG. 1 is a view illustratingthe configuration of an irradiation system, of a particle beam therapysystem, that is provided with a multi-leaf collimator. FIG. 2 is a setof views for illustrating the configurations of a particle beam therapysystem and a multi-leaf collimator when they are viewed from directionsthat are perpendicular to each other with respect to the center (zdirection) of a charged particle beam in FIG. 1; FIG. 2( a) is a sideview when viewed from the y direction; FIG. 2( b) is a side view whenviewed from the x direction. FIG. 3 is to explain the shape of a beambundle in an irradiation system of a particle beam therapy system; FIG.3( a) is a view illustrating the overall appearance of a beam bundle;FIG. 3( b) and FIG. 3( c) are views of the beam bundle when viewed fromdirections that are perpendicular to each other with respect to thecenter (z direction) of a charged particle beam in FIG. 3( a); FIG. 3(b) is a side view when viewed from the y direction; FIG. 3( c) is a sideview when viewed from the x direction. Each of FIGS. 4 and 5 is a set ofviews for explaining the configurations of a multi-leaf collimator and aleaf plate, which is a main constituent member of the multi-leafcollimator, when viewed from various directions.

At first, as an assumption for a detailed explanation about theconfiguration of a multi-leaf collimator, an irradiation system, of aparticle beam therapy system, that includes a multi-leaf collimator willbe explained. As illustrated in FIGS. 1 and 2, a particle beam therapysystem 10 is provided with a wobbler electromagnet 1 (an upstreamwobbler electromagnet 1 a, a downstream wobbler electromagnet 1 b) thatfunctions as an irradiation nozzle for enlarging an irradiation field bycircularly scanning the charged particle beam B, which is supplied froman unillustrated accelerator and has a so-called pencil-looking shape; aridge filter 2 for enlarging the width of a Bragg peak in accordancewith the thickness of an irradiation subject; a range shifter 3 forchanging the energy (range) of the charged particle beam B in accordancewith the depth (irradiation depth) of the irradiation subject; a blockcollimator 4 for limiting the enlarged irradiation field to apredetermined area so as to prevent superfluous irradiation onto normaltissues; a multi-leaf collimator 5 that is configured with a pluralityof leaf plates and a leaf drive mechanism for driving each of the leafplates and that limits an irradiation field in such a way that theirradiation field coincides with the shape of a diseased site; and abolus 6 that limits the range of the charged particle beam B in such away that the range coincides with the depth-direction shape of anirradiation subject.

Next, there will be explained the operation and the principle of anirradiation system that enlarges an irradiation field by means of anirradiation nozzle in which the Wobbling method is utilized. The chargedparticle beam B is accelerated by the unillustrated accelerator; then,as a so-called pencil beam having a diameter smaller than severalmillimeters, it is introduced to the irradiation system through atransport system. The beam introduced to the irradiation system isscanned by the wobbler electromagnet 1 in such a way as to draw acircular orbit. As illustrated in FIG. 1 or 2, the wobbler electromagnet1 is usually provided with an x-direction electromagnet 1 a and ay-direction electromagnet 1 b; the two electromagnets are arranged insuch a way as to be superimposed on each other along the center axisX_(B) of the charged particle beam B. Here, for clarity of description,the x direction and the y direction will be defined. In variousspecifications, coordinate systems are defined; however, in this“DESCRIPTION”, the coordinate system is defined in the following manner.The direction in which the charged particle beam B travels is defined asthe positive direction of the z axis. The x axis and the y axis are axesthat are perpendicular to the z axis; the x axis and the y axis are alsoperpendicular to each other. Then, the xyz coordinate system isestablished in such a way as to be a right-handed coordinate system. Ineach of the examples in FIGS. 1 and 2, the upstream wobblerelectromagnet 1 a and the downstream wobbler electromagnet 1 b scan abeam in the x direction and in the y direction, respectively. Due to thescanning by the electromagnets 1 a and 1 b, the irradiation field isexpanded in the xy direction (planar direction).

The charged particle beam B whose irradiation field has been enlargedpasses through the ridge filter 2. A ridge filter is formed, forexample, in such a way that a great number of cones or plates whosecross sections are triangles are arranged on a plane; assuming that, forexample, an irradiation field is divided into a great number ofsub-areas, in which there exist beams that pass through differentthicknesses from one another. For easier understanding, FIG. 1 or 2illustrates cones that are arranged as in a pin holder (“kenzan”). Insuch a manner as described above, the width of a Bragg peak SOBP(Spread-Out Bragg Peak) is enlarged. That is to say, the ridge filter 2enlarges the irradiation field also in the z direction. Next, thecharged particle beam B whose irradiation field has been enlarged passesthrough the range shifter 3. The range shifter 3 is a device thatchanges the energy of the charged particle beam B. Due to the rangeshifter 3, the enlarged irradiation field can be irradiated onto aposition of a desired inner-body depth. Next, the beam that has passedthrough the range shifter 3 passes through the block collimator 4. Theblock collimator 4 is, for example, a metal block in which a passinghole PH is provided, and limits the planar-direction (the xy plane)spread of the irradiation field. This is because superfluous irradiationonto normal tissues can be prevented by preliminarily limiting theirradiation coverage.

Next, the charged particle beam passes through the multi-leaf collimator5. As described later, through a penetration shape PS formed based onthe positions of a plurality of leaves 5 _(L), the multi-leaf collimator5 limits the shape of the irradiation field in accordance with the shapeof the diseased site. That is to say, the multi-leaf collimator 5performs limitation and formation of the irradiation field in the xydirection. The multi-leaf collimator 5 is provided with at least theplurality of leaf plates 5 _(L) (collectively referred as a leaf group 5_(G)) and a leaf drive mechanism 5 _(D). However, the configuration ofthe leaf drive mechanism 5 _(D) itself is not important, as long as thedriving orbit of a leaf can be specified. If the leaf drive mechanism 5_(D) itself is drawn in a figure, it becomes difficult to illustrate thearrangement of the leaf plates 5 _(L); therefore, in FIGS. 1, 2, andthereafter, for the sake of simplicity, only a leaf plate 5 _(L) or onlythe leaf group 5 _(G) in which the leaf plates 5 _(L) are integrated,out of the multi-leaf collimator 5, is illustrated.

Lastly, the charged particle beam B passes through the bolus 6. Thebolus 6 is a limiter that is formed of resin or the like; it is formedin such a shape as to compensate the depth-direction shape of a diseasedsite, for example, the distal shape of the diseased site. The distalshape denotes the depression-protrusion contour of the deepest portion.In this situation, the energy of the irradiation field is limited(formed in the z direction) to have a shape the same as the distalshape. That is to say, the bolus 6 performs limitation and formation ofthe irradiation field in the z direction.

The function of the irradiation system of a particle beam therapy systemis to form an irradiation field in accordance with the diseased siteonto which a beam is irradiated. In the Wobbling method that is adopted,as the method therefor, in a particle beam therapy system according toEmbodiment 1, an irradiation field is enlarged only by the wobblerelectromagnet 1. For example, the “large-area uniform irradiation methodthrough spiral beam scanning” disclosed in Patent Document 3 is aspecific example of this method, which is referred to as the “spiralWobbling method”, among the Wobbling methods. Briefly speaking, thespiral Wobbling method is to scan a beam in a spiral manner so as toenlarge an irradiation field; the scanning orbit (scanning locus) in theirradiation field is contrived so that the flatness is secured.Additionally, a beam scanning orbit according to the spiral Wobblingmethod can be seen in FIG. 1 and the like of Patent Document 1.

Meanwhile, in general, the method which is referred to as the “Wobblingmethod” often signifies the “single-circle Wobbling method”; in thatcase, when an irradiation field is enlarged, the flatness is secured bymeans of a scatterer. Therefore, among the Wobbling methods, there existnot only a Wobbling method in which a scatterer is utilized but also aWobbling method in which no scatterer is utilized; thus, the directionalbehavior of a beam differs depending on whether or not there exists ascatterer. In the case where a scatterer is utilized, the beam spreadson the whole surface of the scatterer; thus, there exists a width in theirradiation direction of a beam that passes through a given point. Incontrast, in the case where as the spiral Wobbling method, a beam isenlarged only by means of a scanning electromagnet without utilizing anyscatterer, the irradiation direction of the beam that passes through agiven point is a single direction that is determined mainly by theposition thereof with respect to the scanning electromagnet.

FIG. 3 is a set of schematic diagrams illustrating the spreading manner(the shape of a beam bundle F_(B)) in which a beam is enlarged by thecouple of scanning electromagnets 1 in the irradiation system of theparticle beam therapy system 10 according to Embodiment 1. In the spiralWobbling method, the beam is enlarged not in a point-light-source mannerbut in such a manner as illustrated in FIG. 3. For the sake ofsimplicity, the spreading manner of the beam, illustrated in FIG. 3,will be referred to as a “series-of-scanners spreading manner”. In thecase where a beam is enlarged not in a point-light-source manner but ina series-of-scanners spreading manner, a limiter suitable therefor needsto be designed.

The series-of-scanners spread will be explained in more detailhereinafter. As illustrated in FIG. 3, the beam B is irradiated from thetop to the bottom (in the z direction). Originally, the beam B issupplied as a thin beam, which is called a pencil beam. Reference pointsCPa and CPb are set on the beam axis X_(B). The reference point CPa maybe regarded as a position where the upstream wobbler electromagnet 1 a(strictly speaking, a scanning axis A_(Sa)) is disposed; similarly, thereference point CPb may be regarded as a position where the downstreamwobbler electromagnet 1 b (strictly speaking, a scanning axis A_(Sb)) isdisposed.

The upstream wobbler electromagnet 1 a disposed at the reference pointCPa scans the beam B with respect to the reference point CPa. Thescanning direction, of the upstream wobbler electromagnet 1 a, in whichthe beam B is scanned is on a plane (the xz plane) of FIG. 3( b) andpasses through the reference point CPa on the beam axis X_(B); the axisA_(Sa), which is perpendicular to the beam axis X_(B), is the actionaxis (scanning axis) of the upstream wobbler electromagnet 1 a. Thedownstream wobbler electromagnet 1 b disposed at the reference point CPbscans the beam B with respect to the reference point CPb. The scanningdirection, of the downstream wobbler electromagnet 1 b, in which thebeam B is scanned is on a plane (the yz plane) of FIG. 3( c) and passesthrough the reference point CPb on the beam axis X_(B); the axis A_(Sb),which is perpendicular to the beam axis X_(B) and the axis A_(Sa), isthe action axis (scanning axis) of the downstream wobbler electromagnet1 b. In other words, the scanning direction (x) of the upstream wobblerelectromagnet 1 a and the scanning direction (y) of the downstreamwobbler electromagnet 1 b are perpendicular to the beam axis X_(B); thescanning direction (x) of the upstream wobbler electromagnet 1 a and thescanning direction (y) of the downstream wobbler electromagnet 1 b areperpendicular to each other.

Furthermore, the shape of the beam bundle F_(B) will geometrically beexplained with reference to FIG. 3. As illustrated in FIG. 3( b), thereis drawn a vertical (z-direction) line whose top end point is thereference point CPa, and then the reference point CPb is provided at aposition other than the reference point CPa on the vertical line. Thereis obtained a sector Fsa through which the line passes when the line ispivoted by ±α° with respect to the reference point CPa. In the casewhere only the upstream wobbler electromagnet 1 a is utilized, thesector Fsa corresponds to the spread of the beam. Next, the sector Fsais divided into the upper part and the lower part by the reference axisA_(Sb) that passes through the reference point CPb. There is obtained aregion through which the lower part of the sector Fsa passes when thelower part of the sector Fsa is pivoted by ±β with respect to thereference axis A_(Sb). This region is recognized as a sector Fsb in FIG.3( c) and represents the spreading manner (the region through which thebeam B can pass: the beam bundle F_(B)) of the beam B. That is to say,the shape of the beam bundle F_(B) having a series-of-scanners spread isa sector whose x-direction and y-direction curvature radiuses aredifferent from each other.

By considering the shape of the beam bundle F_(B) having aseries-of-scanners spread that is caused by enlarging an irradiationfield by means of two scanning electromagnets 1 a and 1 b whose scanningdirections are different from each other, as described above, themulti-leaf collimator 5 according to Embodiment 1 of the presentinvention is configured for the purpose of accurately forming ahigh-contrast irradiation field without undergoing the effect of apenumbra. In other words, in the multi-leaf collimator 5 according toEmbodiment 1 of the present invention, each of the leaf plates 5 _(L) isconfigured in such a way that the substantial facing side P_(L) facingthe adjacent leaf plate in the thickness direction is formed of a planeincluding the scanning axis A_(sa), of the scanning electromagnet 1 a,that is set at the reference point CPa on the beam axis XB of thecharged particle beam B, and each of the leaf plates 5 _(L) is drivenalong a circumferential orbit with respect to the scanning axis A_(sb)),of the scanning electromagnet 1 b, that is set at the reference pointCPb on the beam axis X_(B) and is perpendicular to the beam axis X_(B)and the scanning axis A_(sa).

Detailed explanation will be made below with reference to FIGS. 4 and 5.FIG. 4 is a set of views for explaining the configurations of amulti-leaf collimator and leaf plates to be driven in the multi-leafcollimator, when the leaves are all closed; FIG. 4( a) is an appearanceperspective view of all the leaf group of the multi-leaf collimator;FIG. 4( b) is a top perspective view of the multi-leaf collimator whenviewed from P direction in FIG. 4( a); FIG. 4( c) is a front perspectiveview of the multi-leaf collimator when viewed from F direction in FIG.4( a); FIG. 4( d) is a side perspective view of a row of leaves in theleft-half portion of the multi-leaf collimator, when viewed from Sdirection in FIG. 4( a). FIG. 5 is a set of views illustrating the statewhere an irradiation field having a predetermined shape is formed; FIG.5( a) is an appearance view of all the leaf group of a multi-leafcollimator; FIG. 5( b) is a top perspective view of the multi-leafcollimator when viewed from P direction in FIG. 5( a); FIG. 5( c) is afront perspective view of the multi-leaf collimator when viewed from Fdirection in FIG. 5( a); FIG. 5( d) is a side perspective view of a rowof leaves in the left-half portion of the multi-leaf collimator, whenviewed from S direction in FIG. 5( a).

As illustrated in FIGS. 4 and 5, the multi-leaf collimator 5 is providedwith a leaf group 5 _(G) that has two leaf rows (5 _(c1) and 5 _(c2):collectively referred to as 5 _(c)), in each of which a plurality ofleaf plates 5 _(L) are arranged in the thickness direction (x direction)in such a way that the end faces E_(L) thereof are trued up, and inwhich the leaf rows 5 _(c1) and 5 _(c2) are arranged in such a way thatthe respective end faces E_(L) thereof face each other and with anunillustrated leaf plate drive mechanism that drives each of the leafplates 5 _(L) in a direction in which that leaf plate approaches theopposed leaf plate or in a direction in which that leaf plate departsfrom the opposed leaf plate; as the shape of the leaf plate 5 _(L), thesubstantial shape of the main face as the plate material of each leafplate, i.e., the facing side P_(L) facing the adjacent leaf plate isformed of a plane including the scanning axis A_(sa) of the scanningelectromagnet 1 a that enlarges the charged particle beam B in the xdirection. In other words, the main plane as the plate material isformed of two planes including the scanning axis A_(sa) of the scanningelectromagnet 1 a; the cross-section of the leaf plate, obtained bycutting the leaf plate along the plane including the irradiationdirection and the board-thickness direction, becomes thicker in adirection from the upstream side of the irradiation direction of thecharged particle beam B to the downstream side thereof.

The drive (in the yz-plane direction) of the leaf plates 5 _(L) is setto be an circumferential orbit O_(L) corresponding to a distance R_(sb)from the scanning axis A_(sb) of the downstream electromagnet 1 b thatenlarges the charged particle beam B in the y direction, and the shapesof an incident-side end face P_(I) that is adjacent to the end faceE_(L) and an emitting-side end face P_(X), among the four end faces ofthe leaf plate 5 _(L), are each formed of an arc whose center is thescanning axis A_(sb)), i.e., each formed as if it is part of a ringwhose center is the scanning axis A_(sb)), so that even when the leafplate 5 _(L) is driven along the circumferential orbit O_(L), thethickness dimension along the irradiation direction of the chargedparticle beam B does not change.

Because of the foregoing configuration, in whichever position the leafplate 5 _(L) is driven, for example, as illustrated in FIG. 5, the endface E_(L) of the leaf plate 5 _(L) that forms the x-direction contourof the penetration shape PS is in parallel with the irradiationdirection of the charged particle beam B that passes through thevicinity of the end face E_(L), whereby no penumbra is caused. Thefacing side P_(L) of the leaf plate 5 _(L) that forms the y-directioncontour of the penetration shape PS is in parallel with the irradiationdirection of the charged particle beam B that passes through thevicinity of the facing side P_(L), whereby no penumbra is caused. Inother words, no penumbra is caused in any contour portion of thepenetration shape PS formed by the multi-leaf collimator 5; therefore,an accurate irradiation field suited to the shape of a diseased site canbe formed.

That is to say, it is only necessary that the thickness-direction shapeand the driving orbit O_(L) of the leaf plate 5 _(L) in the multi-leafcollimator 5 according to Embodiment 1 of the present invention form ashape the same as the spread of the beam bundle F_(B) of the chargedparticle beam B. That is to say, the spread is the passable range at atime when the respective scanning angles of the couple of scanningelectromagnets 1 a and 1 b are limited. Furthermore, the spread is theposition of a charged particle beam at a time when the beam propagationdistance from the beam source is within a given range. Because themulti-leaf collimator 5 is obtained by laminating the leaf plates 5_(L), the formed penetration shape PS is also the spread shape of thebeam bundle F_(B) of a charged particle beam. Moreover, because of theforegoing configuration, whatever the shape of the opening (contour)that forms the penetration shape PS is, the end face E_(L), of the leafplate 5 _(L), that is a wall face of the opening and faces the center ofthe irradiation field and the facing side P_(L) facing the adjacent leafplate are in parallel with the irradiation direction of a chargedparticle beam that passes through the vicinity of those faces.Accordingly, the problem of a penumbra, caused when a couple of scanningelectromagnet 1 a and 1 b are utilized, can be solved. In the case whereirradiation is implemented by use of a scatterer for the purpose ofraising the flatness, a range in the distribution of the irradiationdirections is caused by the foregoing series-of-scanners manner.Accordingly, because even in the case where the multi-leaf collimator 5is utilized, some of charged particle beams hit the end face E_(L) ofthe leaf plate or the facing side P_(L), the effect of suppressing apenumbra is reduced in comparison with the case where no scatterer isutilized; however, it is made possible to obtain a larger effect ofsuppressing a penumbra in comparison with a simple cone-shapedconventional multi-leaf collimator.

In the multi-leaf collimator 5 according to Embodiment 1, thethickness-direction shape and the driving orbit O_(L) are set based onthe position of the upstream electromagnet 1 a and the position of thedownstream electromagnet 1 b, respectively; however, the presentinvention is not limited thereto. They may be set on the oppositepositions. Accordingly, there has been described that the upstreamelectromagnet 1 a and the downstream electromagnet 1 b scan a beam inthe x direction and in the y direction, respectively; however, they mayscan a beam in an opposite manner. Although the drawings illustrate thatthe angles, between the facing sides PL are uniform, that specify thethickness of the leaf plate 5L; however, the present invention is notlimited thereto. Even when the angles are not uniform, it is madepossible to obtain the effect of suppressing a penumbra. The reason whythe expression “substantial” is utilized for the facing side is to meanthat the facing side is a side for distinguishing it from the leaf thatis substantially adjacent to it when the leaves are laminated in thethickness direction; for example, even when a groove or a recess forforming a driving rail is provided in the facing side, it is understoodthat the facing side is formed of a plane including the scanning axisA_(sa) of the scanning electromagnet 1 a set at the reference point CPa.The drawings illustrate the state where one of the leaves 5 _(L) of theleaf row 5 _(c1) and one of the leaves 5 _(L) of the leaf row 5 _(c2)make a pair; however, they do not necessarily need to make a pair. Thenumber of the leaf rows does not need to be two; for example, even whenthe number of the leaf rows is one, it is only necessary that when theend face E_(L) of the leaf plate becomes closest to the beam axis X_(B),the end face E_(L) adheres to the fixed side so as to block the beam B.The number of the leaf rows may be more than two.

As a method of enlarging an irradiation field, there has been explaineda spiral Wobbling method in which a scanning locus becomes a spiral;however, as explained in the following embodiments, another spiralWobbling method may be utilized, and the method may not be limited to aspiral Wobbling method. Moreover, the electromagnet that functions as anirradiation nozzle is not limited to the wobbler electromagnet 1; it isonly necessary that the irradiation nozzle is to enlarge an irradiationfield by means of two electromagnets whose scanning directions aredifferent from each other.

As described above, the multi-leaf collimator 5 according to Embodiment1 is disposed in the charged particle beam B that is irradiated by useof the scanning electromagnet 1 so as to enlarge an irradiation field ofthat, in order to form the irradiation field so as to be conformed tothe shape of a diseased site, which is an irradiation subject; themulti-leaf collimator 5 is provided with the leaf row 5 _(c) in which aplurality of leaf plates 5 _(L) are arranged in the thickness directionin such a way that the end faces E_(L) thereof are trued up and with theleaf plate drive mechanism 5 _(D) that drives each of the leaf plates 5_(L) in such a way that the end face E_(L) thereof approaches or departsfrom the beam axis X_(B) of the particle beam B or that drives each ofthe leaf plates 5 _(L) in a direction in which that leaf plate 5 _(L)approaches the opposed leaf plate or in a direction in which that leafplate 5 _(L) departs from the opposed leaf plate. In each of the leafplates 5 _(L), the facing side P_(L) facing a leaf plate that isadjacent to that leaf plate in the thickness direction (x direction) isformed of a plane P_(sa) including the scanning axis A_(sa), which is afirst axis perpendicular to the beam axis X_(B) and is set at thereference point CPa that is a first position on the beam axis X_(B) ofthe charged particle beam B; the leaf plate drive mechanism 5 _(D)drives the leaf plate 5 _(L) along the circumferential orbit O_(L)around the scanning axis A_(sb), which is a second axis perpendicular tothe beam axis X_(B) and the first axis A_(sa), set at the referencepoint CPb that is a second position on the beam axis X_(B). As a result,the spreading manner of the beam bundle F_(B) of the charged particlebeam B and the directions of the facing side P_(L) and the end faceE_(L) that form the contour of the penetration shape PS of themulti-leaf collimator 5 coincide with each other, so that the effect ofa penumbra is suppressed and hence an accurate irradiation fieldconforming to the shape of an irradiation subject can be formed.

Furthermore, the shapes of the end face P_(I) at the incident side ofthe charged particle beam B and the end face P_(X) at the emitting sidethereof that are adjacent to the end face E_(L), among the main four endfaces of the leaf plate 5 _(L), are formed in the shape of an arc whosecenter is the scanning axis A_(sb)), which is the second axis;therefore, the leaf plate 5 _(L) can readily be driven along thecircumferential orbit O_(L). And whichever position the leaf plate 5L isdriven, the depth dimension along the irradiation direction of thecharged particle beam B does not change; therefore, the distance forshutting off the charged particle beam becomes constant.

The particle beam therapy system 10 according to Embodiment 1 of thepresent invention is provided with the wobbler electromagnet 1, which isan irradiation nozzle that scans the charged particle beam B suppliedfrom an accelerator, by use of two electromagnets 1 a and 1 b whosescanning directions are different from each other and irradiates thecharged particle beam B in such a way as to enlarge an irradiationfield, and the foregoing multi-leaf collimator 5 that is disposed in thecharged particle beam B (the beam bundle FB thereof) irradiated from theirradiation nozzle 1; the multi-leaf collimator 5 is disposed in such away that the first axis thereof coincides with the scanning axis (A_(sa)or A_(sb)) of one of the two electromagnets and the second axis thereofcoincides with the scanning axis (A_(sb) or A_(sa)) of the otherelectromagnet. Therefore, the effect of a penumbra is suppressed andhence a charged particle beam can be irradiated with an accurateirradiation field conforming to the shape of an irradiation subject.

Embodiment 2

In Embodiment 1, there has been described the application of amulti-leaf collimator according to the present invention to the spiralWobbling method in which a beam is scanned in a spiral manner. However,the technical idea of the present invention is not limited to theforegoing scanning orbit shape (scanning locus) in the irradiation fieldof a beam; the effect of the present invention is demonstrated even inthe case of other beam scanning loci, as long as the spreading manner isa series-of-scanners manner. Thus, in Embodiment 2, there will bedescribed a case where a multi-leaf collimator according to the presentinvention is applied to an irradiation system having another typicalbeam scanning locus.

At first, there will be explained a beam scanning locus produced throughthe spiral Wobbling method utilized in Embodiment 1. As disclosed inPatent Document 3, the spiral scanning locus is given by the equation(1) including the following three equalities.

$\begin{matrix}{{{r(t)} = \sqrt{{\frac{R_{\max} - R_{\min}}{\pi\; N}v_{0}t} + R_{\min}^{2}}}{{\omega(t)} = {{\frac{v_{0}}{\sqrt{{\begin{matrix}{R_{\max} - R_{\min}} \\{\pi\; N}\end{matrix}v_{0}t} + R_{\min}^{2}}}\therefore{\theta(t)}} = {{\theta(0)} + {\int_{0}^{t}{{\omega(\tau)}\ {\mathbb{d}\tau}}}}}}} & (1)\end{matrix}$where R_(min) is the radius at a time when the time t=0, R_(max) is theradius at a time when the time t=T, and N is the scanning rotationspeed. In addition, r(t) is the radial-direction coordinates, and θ(t)is the angle-direction coordinates; r(t) and θ(t) are representedthrough a polar coordinate system.

The shape of the beam scanning locus given by the equation (1) isspiral; the shape is effective in obtaining a uniform dose distributionby scanning a beam within a circular region. However, it is not requiredthat in order to obtain a uniform dose distribution, the beam scanninglocus is limited to a spiral locus. It is conceivable that the beamscanning loci for obtaining a uniform dose distribution through scanningby two electromagnets can be categorized into a number of typicalpatterns.

The Wobbling method is to form a uniform dose distribution bycontinuously scanning a beam. That is to say, it is desirable that thebeam scanning locus in the Wobbling method is continuous and periodical.Thus, there has been studied a pattern in which a beam orbit isrepresented by a polar coordinate system and r(t) and θ(t) arecontinuously and periodically changed.

<Typical Pattern-1>

In the first pattern, r(t) and θ(t) are each defined as a function thatchanges continuously and periodically, as described below.

r(t)=continuous and periodic function (period: T₁)

θ(t)=continuous and periodic function (period: T₂)

In this situation, the respective periods of r(t) and θ(t), which aredifferent from each other, may be utilized. Attention should be drawn tothe fact that as for the angle θ, 360° can be regarded as 0° as itrotates once. In other words, 360° continues to 0°. When represented inradian, 2π can be regarded as 0.

Examples that realize the foregoing pattern include such a beam scanninglocus as represented by the equation (2) including the following threeequalities.r(τ)=r ₁ +r ₂ sin(ω_(r)τ+φ_(r))θ(τ)=ω_(θ)ττ=τ(t)  (2)where τ(t) is the parameter of the equation (2) that is represented byutilizing a parameter, and is the function of the time. ω_(r) is theangular velocity that determines r(t), and the period of r(t) is2π/ω_(r). φ_(r) is the initial phase. ω_(θ) is the angular velocity thatdetermines θ(t), and the period of θ(t) is 2π/ω_(θ).

FIG. 6 represents an example of beam scanning locus ST1 generatedaccording to the equation (2). FIG. 6 represents a scanning locus on agiven plane that is perpendicular to the beam axis; the abscissa denotes“x” and the ordinate denotes “y”; x and y are each normalized. Thereason why in the equation (2), the parameter is not the time is that itis required to make the drawing speed changeable depending on the place.For example, in FIG. 6, beam scanning concentrates in the vicinity ofthe center of the beam axis represented as the coordinates (0, 0); thus,in a portion in the vicinity of the center portion where the locusconcentrates, contrivance such as raising the scanning speed is made sothat a uniform dose distribution is obtained.

<Typical Pattern-2>

In the second pattern, two or more functions for defining a drawingpattern are combined so that a beam scanning locus is formed. Forexample, a function for drawing a large circle is combined with afunction for drawing a small circle. An example is represented by theequation (3) including the following three equalities.x(τ)=r ₁ cos(ω₁τ+φ₁)+r ₂ cos(ω₂τ+φ₂)y(τ)=r ₁ sin(ω₁τ+φ₁)+r ₂ sin(ω₂τ+φ₂)τ=τ(t)  (3)where x(τ) and y(τ) are the x coordinate and the y coordinate,respectively, of a beam scanning locus; they are represented by use ofan orthogonal coordinates system. FIG. 7 represents an example of beamscanning locus generated according to the equation (3). As is the casewith FIG. 6, FIG. 7 represents a scanning locus on a given plane that isperpendicular to the beam axis; the abscissa denotes “x” and theordinate denotes “y”; x and y are each normalized.

Among toys, there exists a tool in which a gear-shaped disk is disposedin a circular hole inside of which teeth are formed; a geometricalpattern is drawn by inserting a pen tip into a small hole provided at apredetermined position in the disk and rolling the disk along thecircular hole. A geometrical pattern generated with the tool alsobelongs to this category. A curve drawn with this tool is referred to asa hypotrochoid; geometrically, the curve is defined as a locus drawn bya fixed point that is lr away from the center of a circle of a radius rwhen the circle of a radius r rolls without sliding along the innercircumference of a circle of a radius kr. In many mixing devices, thecurve is adopted as the driving pattern for a mixing unit. The reasonwhy the parameter is not the time t is that it is required to make thedrawing speed changeable depending on the place, as is the case with theabove example.

As described above, in the method in which through a wobblerelectromagnet, a continuous and periodical pattern (line drawing) isdrawn, the pattern is not necessarily a spiral. However, the idea inwhich by utilizing no scatterer but by contriving a beam orbit,large-area uniform irradiation is realized originates in the “spiralWobbling method”; therefore, in some cases, each of these methodsdescribed in Embodiment 2 is also referred to as a broad-sense spiralWobbling method. In addition, also in these broad-sense spiral Wobblingmethods, a beam spreads not in a point-light-source manner but in aseries-of-scanners manner.

In other words, also in the particle beam therapy system having anirradiation system utilizing the broad-sense spiral Wobbling methodaccording to Embodiment 2, by utilizing the multi-leaf collimatordescribed in Embodiment 1, the thickness-direction shape of the leafplate and the driving orbit can be made the same as the spread of thebeam bundle F_(B) of the charged particle beam B. Accordingly, theformed penetration shape PS becomes the same as the shape of the beambundle F_(B) of the charged particle beam B; thus, whatever the shape ofthe opening that forms the penetration shape PS is, the end face that isa wall face of the opening and faces the center of the irradiation fieldand the facing side facing the adjacent leaf plate coincide with theirradiation direction of a charged particle beam. Accordingly, theproblem of a penumbra, caused when a couple of scanning electromagnetsare utilized, can be solved.

Embodiment 3

In each of Embodiments 1 and 2, there has been described a case where amulti-leaf collimator is applied to irradiation through the Wobblingmethod. However, as described above, the irradiation method itself isnot essential and does not define the technical idea of the presentinvention. With regard to a particle beam therapy system, there has beenproposed a spot-scanning method in which a charged particle beam isscanned by means of a couple of scanning electromagnets, and a spot isirradiated onto an irradiation subject in a pointillism manner. Also inthe spot-scanning method, a beam spreads in a series-of-scanners manner.Therefore, in the case where a multi-leaf collimator is utilized in spotscanning, there is demonstrated an effect that a penumbra is suppressedand a high-contrast irradiation field is formed.

Embodiment 4

In Embodiment 3, there has been described the application of amulti-leaf collimator according to the present invention to thespot-scanning method. There exists a raster-scanning method in which acharged particle beam is scanned by means of a couple of scanningelectromagnets, as is the case with a spot-scanning method, and rasterirradiation is performed onto an irradiation subject in a one-strokewriting manner. Also in the raster-scanning method, a beam spreads in aseries-of-scanners manner. Therefore, in the case where a multi-leafcollimator is utilized in the raster-scanning method, the multi-leafcollimator 5 according to the foregoing embodiment demonstrates aneffect. In other words, also in the case where an irradiation field isenlarged through a scanning method such as the spot-scanning method orthe raster-scanning method, when the multi-leaf collimator 5 accordingto the embodiments of the present invention is utilized, there isdemonstrated an effect that a penumbra is suppressed and a high-contrastirradiation field is formed.

Embodiment 5

There has been proposed a particle beam therapy system in which, forexample, as disclosed in Patent Document 4, one of two scanningelectromagnets is omitted, by contriving control method for a deflectionelectromagnet. However, even in the case of such an irradiation system,a deflection electromagnet for changing the orbit direction (thedirection of the beam axis) replaces the omitted scanning electromagnetthat scans a charged particle beam; therefore, the beam bundle has aseries-of-scanners spread, whereby the multi-leaf collimator accordingto each of the foregoing embodiments demonstrates an effect ofsuppressing a penumbra.

FIG. 8 is a view illustrating an irradiation system including amulti-leaf collimator in a particle beam therapy system according toEmbodiment 5. In FIG. 8, the beam axis of a charged particle beam Bsupplied in the horizontal direction (the x direction) is deflected tothe vertical direction by a deflection electromagnet 201 a and passesthrough a scanning electromagnet 201 b; then, as is the case inEmbodiment 1, the charged particle beam B is irradiated onto anirradiation subject, by way of a ridge filter 2, a range shifter 3, aring collimator 4, a multi-leaf collimator 205, and the bolus 6. Theconfiguration of a particle beam therapy system 210 according toEmbodiment 5 is the same as that of Embodiment 1, excluding the factthat instead of the scanning electromagnet 1 a in the particle beamtherapy system 10 according to Embodiment 1, the deflectionelectromagnet 201 a is provided and that the setting reference for theshape and the orbit of the leaf plate of the multi-leaf collimator 205is different.

In FIG. 8, inside the deflection electromagnet 201 a, the chargedparticle beam B supplied in the horizontal direction is deflected in thez direction, while the beam axis P_(X) draws an arc. In this situation,in the case of a normal deflection electromagnet, because control isperformed in such a way that the magnetic field becomes constant, thebeam bundle of the charged particle beam B does not spread; however, byperiodically changing the magnetic field, the deflection electromagnet201 a scans the charged particle beam B in the x direction so that thebeam bundle can spread in the x direction from P_(E1) to P_(E2). Inother words, the deflection electromagnet 201 a plays the role of theupstream scanning electromagnet 1 a of Embodiment 1. The portionthereafter is basically the same as Embodiment 1; the scanningelectromagnet 201 b further spreads the beam bundle, which has beenspread in the x direction, in the y direction.

This beam spreading manner can be regarded as a spreading manner at atime when the scanning axis of the upstream scanning electromagnet 201 aexists at an equivalent reference point E_(AS) in FIG. 8 and a beam,irradiated from the upper side along the beam axis E_(x), is scanned inthe x direction (including the z-direction component) and spreads in thex direction from E_(E2) to E_(E2). Because inside the deflectionelectromagnet 201 a, the beam axis is gradually deflected as the beamadvances, the beam axes (=beam axis E_(x)) at the entrance side and atthe exit side are different from each other; thus, a scanning axisE_(As) exists off the deflection electromagnet 201 a. However, becausethe axis of a beam that enters the multi-leaf collimator 205 is the beamaxis E_(X), the reference point CPa that specifies the position of thescanning axis E_(As) can be regarded as existing on the beam axis of thebeam that enters the multi-leaf collimator 205, as a manner of thinking;therefore, the scanning axis E_(As) can also be regarded as beingperpendicular to the beam axis of the beam that enters the multi-leafcollimator 205. Accordingly, also in an irradiation system in which oneof the electromagnets that perform scanning also plays the role of adeflection electromagnet, it may be allowed that the equivalent scanningaxis E_(As) is calculated based on the manner of beam spreading withrespect to the beam axis of the beam that enters a multi-leafcollimator, and as is the case in Embodiment 1, the shape of the leafplate of the multi-leaf collimator 205 and the orbit are set based onthe equivalent scanning axis E_(As) and the scanning axis A_(sb) (thereference point CPb).

As can be seen from FIG. 8, in the case of an irradiation system inwhich one of the scanning electromagnets is omitted and instead of theomitted scanning electromagnet, the deflection electromagnet 201 a thatbends the orbit is utilized, the distance between the reference pointCPb and the reference point (equivalent) CPa that specifies theequivalent scanning axis E_(As) is wide in comparison with an ordinaryirradiation system in which scanning is performed by an electromagnetdedicated to scanning (e.g., 1 a and 1 b in Embodiment 1). Accordingly,in the case of a multi-leaf collimator in which a beam is assumed tospread in a point-light-source manner, there is more conspicuously poseda problem that a penumbra is caused. However, the shape and the orbit ofthe leaf plate of the multi-leaf collimator 205 according to Embodiment5 of the present invention are set in such a way that whateverpenetration shape is formed, the direction of the plane on which thecontour of the penetration shape is formed is the same as the directionof the beam spread. Therefore, the problem of a penumbra, which isconspicuously caused with an irradiation system in which one of thescanning electromagnets is omitted, can readily be solved.

As described above, in the particle beam therapy system 210 according toEmbodiment 5, it is configured in such a way that scanning for onedirection (x or y) out of the x-direction scanning and y-directionscanning is performed by the deflection electromagnet 201 a thatdeflects the direction of a beam axis, and by regarding that the beamaxis for setting the reference points CPa and CPb is the beam axis E_(X)of the beam that enters the multi-leaf collimator 205, the configurationand the positioning of the multi-leaf collimator 205 are implemented;therefore, a penumbra can be suppressed and hence a high-contrastirradiation field can be formed.

Embodiment 6

In each of Embodiments 1 through 5, there have been explained theconfigurations of a multi-leaf collimator and an irradiation systemutilizing the multi-leaf collimator and the beam orbit in theirradiation system. In Embodiment 6, there will be explained a treatmentplanning apparatus in which the operation conditions of a multi-leafcollimator and a particle beam therapy system according to each of theforegoing embodiments of the present invention are set.

Here, before explaining a treatment planning apparatus, there will beexplained medical practice on which a treatment plan to be implementedby the treatment planning apparatus is based. In general, it isconceivable that medical practice is configured with a number of stages.FIG. 9 represents the stages (flow) of medical practice by a flowchartand describes one or more apparatuses utilized in each stage. Withreference to FIG. 9, the flow of a medical practice will be explained.

Specifically, medical practice may be roughly configured with apreventive diagnosis stage (MS1), a diagnosis stage (MS2), a treatmentplanning stage (MS3), a treatment stage (MS4), and arehabilitation/follow-up stage (MS5). In particular, in a particle beamtherapy or the like, the respective apparatuses utilized in theforegoing stages are those described in the right column of FIG. 9. Forexample, the apparatuses utilized in the diagnosis stage (MS2) are anX-ray image-capturing device, a CT (Computed Tomography), an MRI(Magnetic Resonance Imaging); the apparatus utilized in the treatmentplanning stage (MS3) is the one that is called a treatment planningapparatus. In addition, the apparatuses utilized in the treatment stage(MS4) are a radiation therapy system and a particle beam therapy system.

Next, each of the stages will be explained.

The preventive diagnosis stage (MS1) denotes a stage where a diagnosisis implemented preventively, regardless of whether or not there has beenshown the onset of a disease. For example, a regular health check and acomplete physical examination fall into this stage; with regard to acancer, a method utilizing fluoroscopic imaging such as radiology, amethod utilizing tomography such as PET (Positron Emission Tomography)or PET/CT, and a method utilizing a genetic test (immunological test)are known.

The diagnosis stage (MS2) denotes a stage where a diagnosis to befollowed by a treatment is implemented after the onset of a disease. Inthe case of particle beam therapy, in order to implement a treatment,three-dimensional information on the position and the shape of adiseased site is required. Accordingly, there are utilized various kindsof CT and MRI that are capable of obtaining three-dimensional data on adiseased site.

The treatment planning stage (MS3) denotes a stage where a treatmentplan is generated based on the result of the diagnosis. In the case ofparticle beam therapy, a treatment plan is generated, in this stage, bya treatment planning apparatus according to Embodiment 6. The treatmentplanning apparatus will be explained in detail later; here, the residualstage will be explained.

The treatment stage (MS4) denotes a stage where an actual treatment isperformed based on the result of the treatment plan. In the case ofparticle beam therapy, a particle beam therapy system is utilized inthis stage. A multi-leaf collimator according to each of the foregoingembodiments is utilized for forming an irradiation field in theirradiation system of a particle beam therapy system. In addition, insome cases, the treatment stage is completed with a single irradiation;however, usually, there are implemented a plurality of irradiations,each irradiation of which is performed every certain period.

The rehabilitation/follow-up stage (MS5) literally denotes a stage whererehabilitation is performed or there is performed a follow-up to checkwhether or not a disease has recurred. In the case of a cancer, in afollow-up of this stage, as is the case in the preventive diagnosisstage, a method utilizing fluoroscopic imaging such as radiology, amethod utilizing tomography such as PET or PET/CT, or a method utilizinga genetic test (immunological test) is adopted.

As described above, in medical practice, the treatment planning is aseries of works performed after the diagnosis stage and before thetreatment stage. In a particle beam therapy system, a charged particlebeam is irradiated based on a treatment plan obtained through atreatment planning apparatus; therefore, a treatment planning apparatusin particle beam therapy is provided with units that approximately playthe following roles.

Role A: a unit for generating three-dimensional data, based on aplurality of image information items for an irradiation subject, whichare preliminarily obtained.

Role B: a unit for generating an optimum irradiation condition(treatment planning draft) under given requirements.

Role C: a unit for simulating and displaying a final dose distributionfor the optimum result (treatment planning draft).

In other words, a treatment planning apparatus is provided with a rolein which in response to the result of a diagnosis, irradiation conditionrequired for treatment is set; furthermore, the treatment planningapparatus has a unit that plays a role D of generating control data forthe particle beam therapy system and the like, based on the setcondition.

In order to play the foregoing roles, the treatment planning apparatusis specifically provided with the following functions.

<Role A>

Function a: a function for generating three-dimensional data based on atomographic image obtained in the diagnosis stage.

Function b: a function for displaying the generated three-dimensionaldata as seen from various viewing points, as is the case with athree-dimensional CAD.

Function c: a function for distinguishing a diseased site from normaltissues and storing them in the generated three-dimensional data.

<Role B>

Function d: a function for setting parameters for a particle beamtherapy system utilized in the treatment stage and for simulatingirradiation.

Function e: a function for optimizing irradiation under the requirementsset by a user of the apparatus.

<Role C>

Function f: a function for displaying the optimized irradiation resultin such a way as to be superimposed on the three-dimensional data.

<Role D>

Function g: a function for setting the shapes, of a multi-leafcollimator and a bolus, for realizing the optimized irradiation (thisfunction is a one when broad-beam irradiation is anticipated, andincludes a case of multi-port irradiation).

Function h: a function for setting the beam irradiation orbit forrealizing the optimized irradiation (when scanning irradiation isanticipated).

Function i: a function for generating a driving code, for a particlebeam therapy system, for realizing the beam irradiation orbit.

<Others>

Function j: a function for storing various kinds of data items generatedin the apparatus.

Function k: a function capable of reading various kinds of data itemsstored in the past and reusing past information.

There will be explained the system configuration of a treatment planningapparatus for realizing the foregoing functions. In recent years, almostno manufacturer of a treatment planning apparatus has designed andmanufactured dedicated hardware; the hardware is configured based on acommercially available Unix (registered trademark) workstation or a PC,and as peripheral devices, universal devices are utilized in many cases.That is to say, manufacturers of treatment planning apparatusesprimarily develop, manufacture, and sell treatment planning software. Inthe treatment planning software, for example, there is prepared a modulefor realizing the functions a through k, as a subprogram to be called bymain program. By omitting, as may be necessary, the flow between thefunction a and the function k or re-implementing it by changing therequirements, the user of a treatment planning apparatus can generate atreatment plan while calling necessary modules.

Next, while advancing the explanation to the functions or the modulesfor realizing those functions, there will be explained a treatmentplanning apparatus according to Embodiment 6.

Function a (module a) generates three-dimensional data based on a seriesof tomographic images obtained in the diagnosis stage. It is desirablethat when a tomographic image is read, patient information such as apatient ID and scanning information (such as a slice interval, a slicethickness, FOV, and a tomographic condition) are also read in acorresponding manner. Here, the three-dimensional data denotesinformation required for virtually and three-dimensionally reproducingan imaging subject including a diseased site in a treatment planningapparatus. In general, there is utilized a method in which a virtualspace is defined in a treatment planning apparatus, points are arrangedwithin the virtual space in such a way as to be spaced evenly apart fromone another and in a lattice-like manner, and the respective materialinformation items, which are obtained from a tomographic image, arepositioned at the corresponding points. The reason why Function a isrequired is that one of the biggest objects of a treatment planningapparatus is to simulate treatment, and for that purpose, it isnecessary to reproduce a diseased site, which is an irradiation subject,and the peripheral tissues thereof.

Function b (module b) displays the generated three-dimensional data asseen from various viewing points, as is the case with athree-dimensional CAD.

Function c (module c) distinguishes a diseased site from normal tissuesand stores them in the generated three-dimensional data. For example, itis assumed that a tomographic image is obtained through X-ray CT. Inthis case, the “material information” utilized in Function a correspondsto the radiolucency of an X-ray. That is to say, the three-dimensionalmodel reproduced in the virtual space from this tomographic imagerepresents the shape of a three-dimensional body formed of materialswhose radiolucencies are different from one another. In the virtualspace of a treatment planning apparatus, the “material information”,i.e., the X-ray radiolucency is rendered by changing the color and thebrightness. Furthermore, this “material information” makes it possibleto understand that this part of the three-dimensional model reproducedin the virtual space corresponds to a bone or that part corresponds to atumor, and a diseased site is distinguished from normal tissues. Theresult of the distinction between a diseased site and normal tissues canbe stored in a storage device (such as a hard disk) of the treatmentplanning apparatus.

Function d (module d) sets parameters for a particle beam therapy systemutilized in the treatment stage and simulates irradiation. Theparameters for a particle beam therapy system denote geometricinformation on the particle beam therapy system and information on anirradiation field. The geometric information includes the position ofthe isocenter, the position of the bed, and the like. The information onan irradiation field includes the foregoing “coordinates of thereference point CPa and the coordinates of the reference point CPb” andthe like. The parameters include the width (thickness) of the leaf plate5 _(L) of the multi-leaf collimator 5 or 205 (hereinafter, only “5”,representing both, is expressed), the number of the leaf plates 5 _(L),the traveling distance (angle) of the leaf plate 5 _(L), and the like.

Function e (module e) optimizes irradiation under the requirements setby a user of the treatment planning apparatus.

Function f (module f) displays the optimized irradiation result in sucha way as to be superimposed on the three-dimensional data.

Function g (module g) sets the shapes, of the multi-leaf collimator 5and the bolus 6, for realizing the optimized irradiation. This functionis a one when broad-beam irradiation is anticipated, and includes a caseof multi-port irradiation.

Function h (module h) sets the beam irradiation orbit for realizing theoptimized irradiation. This function is a one when scanning such as spotscanning or raster scanning is anticipated.

Function I (module i) generates a driving code, for a particle beamtherapy system, for realizing the beam irradiation orbit. In thissituation, when as described later, a coordinate system conforming to aseries-of-scanners spread is adopted, there can readily be generated adriving code for realizing an opening shape (penetration shape SP)corresponding to the obtained optimum irradiation plan for themulti-leaf collimator 5 according to each of Embodiments 1 through 5.

Function j (module j) stores various kinds of data items set andgenerated in the apparatus.

Function k (module k) can read various kinds of data items stored in thepast and reuse past information.

<Coordinate System Conforming Series-of-Scanning Spread>

In a conventional treatment planning apparatus, the three-dimensionaldata utilized in Function a and functions following to Function a arerepresented by an orthogonal coordinate system (xyz coordinate system).In the case of a multi-leaf collimator whose total shape is aconventional rectangular parallelepiped, the leaf driving directionthereof is also represented by an orthogonal-coordinate direction (forexample, the x direction and the y direction); therefore, it isconvenient to represent the three-dimensional data by an orthogonalcoordinate system. That is because leaf driving data and shape data forgenerating the shape of the opening portion in such a way as to coincidewith the shape of a diseased site coincide with each other.

On the other hand, in the case of the multi-leaf collimator 5 accordingto the present invention, it is desirable that because the drive of theleaf plate 5L is performed in a curvilinear manner, the command valuefor driving the leaf is given as an angle with respect to the referencepoint. That is to say, it is desired that the shape data for forming theshape of the opening portion in accordance with the shape of a diseasedsite includes an angle, with respect to the reference point, that is inthe same format as the leaf driving command value of the presentinvention.

Thus, the treatment planning apparatus according to Embodiment 6 of thepresent invention is configured in such a way that the three-dimensionaldata for a diseased site is represented by a special coordinate system.

Specifically, it is a special coordinate system represented by thefollowing definition (D1).[ψ_(a),ψ_(b) ,r _(b)]  (D1)where ψ_(a) is a beam deflection angle with respect to the referenceaxis (A_(sa)) that is perpendicular to the beam axis X_(B) and passesthrough the reference point CPa, ψ_(b) is a beam deflection angle withrespect to the reference axis (A_(sb)) that is perpendicular to the beamaxis X_(B) and the reference axis A_(sa) and passes through thereference point CPb, and r_(b) is a distance between the reference pointCPb (or the reference axis A_(sb))) and the irradiation point.

An arbitrary point in the three-dimensional space can uniquely berepresented by the foregoing three information items. In this regard,however, it is required to preliminarily determine the reference pointsCPa and CPb in accordance with the arrangement of the scanningelectromagnets 1 a and 1 b. Instead of r_(b), there may be utilized abeam propagation distance r_(a) between the reference point CPa (or thereference axis (Asa)) and the irradiation point.

Here, it is assumed that the isocenter, which is an irradiationreference, is utilized as the origin of the xyz coordinate system, andthe xyz coordinates of the reference point CPa and the xyz coordinatesof the reference point CPb are given as follows.

reference point CPa: (0, 0, −1_(a))

reference point CPb: (0, 0, −1_(b))

Then, it is assumed that as illustrated in FIGS. 1 through 3, theupstream scanning electromagnets 1 a and the downstream scanningelectromagnet 1 b are the x-direction scanning electromagnet and they-direction scanning electromagnet, respectively. In this situation,when the coordinates of a certain point is given by [ψ_(a), ψ_(b),r_(b)] represented by use of the special coordinate system described inthe definition (D1), the x coordinate, the y coordinate, and the zcoordinate of this point are given by the following equation (4).

$\begin{matrix}{\begin{bmatrix}x \\y \\z\end{bmatrix} = {{{{Rot}_{x}( \varphi_{b} )}\{ {{{{Rot}_{y}( \varphi_{a} )}\begin{bmatrix}0 \\0 \\{l_{a} - l_{b} + r_{b}}\end{bmatrix}} - \begin{bmatrix}0 \\0 \\{l_{a} - l_{b}}\end{bmatrix}} \}} - \begin{bmatrix}0 \\0 \\l_{b}\end{bmatrix}}} & (4)\end{matrix}$

Here, when Rot_(x)(ψ_(b)), and Rot_(y)(ψ_(a)) in the equation (4) aredefined as in (D2), the xyz coordinates of this certain point isobtained as in the equation (5).

$\begin{matrix}{{{{Rot}_{x}( \varphi_{b} )} = \begin{bmatrix}1 & 0 & 0 \\0 & {\cos\;\varphi_{b}} & {{- \sin}\;\varphi_{b}} \\0 & {\sin\;\varphi_{b}} & {\cos\;\varphi_{b}}\end{bmatrix}},{{{Rot}_{y}( \varphi_{a} )} = \begin{bmatrix}{\cos\;\varphi_{a}} & 0 & {\sin\;\varphi_{a}} \\0 & 1 & 0 \\{{- \sin}\;\varphi_{a}} & 0 & {\cos\;\varphi_{a}}\end{bmatrix}}} & ( {D\; 2} ) \\\begin{matrix}{\begin{bmatrix}x \\y \\z\end{bmatrix} = {{{{Rot}_{x}( \varphi_{b} )}\{ {\begin{bmatrix}{( {l_{a} - l_{b} + r_{b}} ){\sin( \varphi_{a} )}} \\0 \\{( {l_{a} - l_{b} + r_{b}} )\cos\;( \varphi_{a} )}\end{bmatrix} - \begin{bmatrix}0 \\0 \\{l_{a} - l_{b}}\end{bmatrix}} \}} - \begin{bmatrix}0 \\0 \\l_{b}\end{bmatrix}}} \\{= {\begin{bmatrix}{( {l_{a} - l_{b} + r_{b}} ){\sin( \varphi_{a} )}} \\{{- {\sin( \varphi_{b} )}}\{ {{( {l_{a} - l_{b} + r_{b}} ){\cos( \varphi_{a} )}} - ( {l_{a} - l_{b}} )} \}} \\{{\cos( \varphi_{b} )}\{ {{( {l_{a} - l_{b} + r_{b}} ){\cos( \varphi_{a} )}} - ( {l_{a} - l_{b}} )} \}}\end{bmatrix} - \begin{bmatrix}0 \\0 \\l_{b}\end{bmatrix}}} \\{= \begin{bmatrix}{( {l_{a} - l_{b} + r_{b}} ){\sin( \varphi_{a} )}} \\{{- {\sin( \varphi_{b} )}}\{ {{( {l_{a} - l_{b} + r_{b}} ){\cos( \varphi_{a} )}} - ( {l_{a} - l_{b}} )} \}} \\{{{\cos( \varphi_{b} )}\{ {{( {l_{a} - l_{b} + r_{b}} ){\cos( \varphi_{a} )}} - ( {l_{a} - l_{b}} )} \}} - l_{b}}\end{bmatrix}}\end{matrix} & (5)\end{matrix}$

On the contrary, the method of obtaining the special coordinate systemfrom the xyz coordinate system is described below.

Because l_(b) is a given value that is inherent to an irradiationsystem, ψ_(b) can be obtained, as in the equation (6), from therelationship between y and z in the equation (5).

$\begin{matrix}{\frac{- y}{z + l_{b}} = {\frac{\sin\;\varphi_{b}}{\cos\;\varphi_{b}} = {{{\tan\;\varphi_{b}}\therefore\varphi_{b}} = {\arctan( \frac{- y}{z + l_{b}} )}}}} & (6)\end{matrix}$

Because being also a given value that is inherent to an irradiationsystem, l_(a) can be defined, as in the definition (D3), from therelationship between y and z in the equation (5); thus, from therelationship with z in the equation (5) and the definition (D3), ψ_(a)can be obtained from the equation (7).

$\begin{matrix}\begin{matrix}{\Lambda:={y^{2} + ( {z + l_{b}} )^{2} + ( {l_{a} - l_{b}} )}} \\{= {( {l_{a} - l_{b} + r_{b}} )\cos\;\psi_{a}}}\end{matrix} & ( {D\; 3} ) \\{\frac{x}{\Lambda} = {\frac{\sin\;\varphi_{a}}{\cos\;\varphi_{a}} = {{{\tan\;\varphi_{a}}\therefore\varphi_{a}} = {\arctan( \frac{x}{\Lambda} )}}}} & (7)\end{matrix}$

Lastly, r_(b) can be obtained from the equation (8).x ²+Λ2=(l _(a) −l _(b) +r _(b))²∴r _(b)=√{square root over (x ²+Λ²)}−(l _(a) −l _(b))  (8)

There is provided a coordinate transformation function in which thecoordinate system [ψ_(a), ψ_(b), r_(b)] conforming to the foregoingseries-of-scanners spread is utilized already from the stage of Functiona, i.e., as Function a or as an auxiliary function for implementingFunction a, there is performed transformation to a special coordinatesystem, under the assumption of series-of-scanners.

For example, FIG. 10 illustrates, with a block diagram, thecharacteristic parts in the roles (units) and the functions (modules) ofa treatment planning apparatus according to Embodiment 6 of the presentinvention. In FIG. 10, a treatment planning apparatus 20 is providedwith a three-dimensional data generation unit 21 for generatingthree-dimensional data from image data on a diseased site, which is anirradiation subject; the irradiation condition setting unit 22 forsetting an irradiation condition, based on the generatedthree-dimensional data; and a control data generation unit 23 forgenerating control data for a particle beam therapy system, based on theset irradiation condition. As described above, these units and modulesare formed in a computer by software; thus, these parts are notphysically formed.

The three-dimensional data generation unit 21 is provided with athree-dimensional data generation module 21 _(M1) for, as Function a,generating three-dimensional data on a diseased site, a body shape, andthe like; a coordinate transformation module 21 _(M2) for transformingthe generated three-dimensional data into data in the coordinate system[ψ_(a), ψ_(b), r_(b)] represented through the definition (D1) under theassumption of series-of-scanners; a display data generation module 21_(M3) for, as Function b, generating display data, based on thetransformed data; and an irradiation subject separation module 21 _(M4)for distinguishing a diseased site, which is an irradiation subject,from normal tissues, based on the transformed data. As Role A, thethree-dimensional data generation unit 21 generates, from imageinformation, three-dimensional data in the coordinate system representedthrough the definition (D1).

As Function B, the irradiation condition setting unit 22 sets, throughthe functions d and e, an optimum irradiation condition, based onthree-dimensional data in the coordinate system represented through thedefinition (D1). The control data generation unit 23 is provided with apenetration shape setting module 23 _(M1) that sets, as the function g,the penetration shape PS to be formed by the multi-leaf collimator 5based on at least the set irradiation condition; and a driving codegeneration module 23 _(M2) that generates, as the function i, arespective driving code for the leaf plates 5L of the multi-leafcollimator 5 based on the set penetration shape. As Role D, the controldata generation unit 23 generates at least control data for themulti-leaf collimator 5 in the coordinate system represented through thedefinition (D1), based on the set irradiation condition.

Accordingly, in the three-dimensional data generation unit 21 and theirradiation condition setting unit 22, three-dimensional data, in thecoordinate system represented through the definition (D1), fordetermining the irradiation position is specified by use of a beamdeflection angle with respect to the reference axis (A_(sa)) that isperpendicular to at least the beam axis X_(B) and passes through thereference point CPa, and a beam deflection angle with respect to thereference axis (A_(sb)) that is perpendicular to the beam axis X_(B) andthe reference axis A_(sa) and passes through the reference point CPb.Thus, the driving code for the multi-leaf collimator 5 generated by thecontrol data generation unit 23 becomes such a driving code as realizesthe opening shape (penetration shape PS) conforming to the optimumirradiation plan obtained in the irradiation condition setting unit 22.In other words, in the treatment planning apparatus 20 according toEmbodiment 6 of the present invention, a function for conversion into aspecial coordinate system in which series-of-scanners is anticipated isprovided in the functions (modules) for playing the roles of a treatmentplan, and three-dimensional data is specified in the special coordinatesystem. As a result, the shape data for generating the shape of theopening portion in accordance with the shape of a diseased site and theleaf driving command value can be represented by a same format includingangles with respect to the reference point (one of the angles is forselecting the leaf plate 5L, among the leaf rows 5 c, that has a facingside PL whose angle is near to the angle). Accordingly, in anirradiation system in which a beam spreads in a series-of-scannersmanner, a driving code for optimally controlling the multi-leafcollimator 5 can readily be generated.

Therefore, in the treatment planning apparatus 20 according toEmbodiment 6 of the present invention, for a particle beam therapysystem utilizing the foregoing multi-leaf collimator 5 (or 205) capableof suppressing a penumbra for an irradiation system in which a particlebeam spreads in a series-of-scanners manner, the leaf driving commandvalue for forming the shape of the opening portion in accordance withthe shape of a diseased site can be generated by directly utilizing thethree-dimensional data inputted to and outputted from the treatmentplanning apparatus 20.

As described above, the treatment planning apparatus 20 according toEmbodiment 6 is configured in such a way as to include thethree-dimensional data generation unit 21 for generatingthree-dimensional data from image data on a diseased site, which is anirradiation subject; the irradiation condition setting unit 22 forsetting an irradiation condition, based on the generatedthree-dimensional data; and the control data generation unit 23 forgenerating at least the control data, among control data items for aparticle beam therapy system, that is for the multi-leaf collimator 5according to one of Embodiments 1 through 5, based on a set irradiationcondition. In addition, the treatment planning apparatus 20 according toEmbodiment 6 is configured in such a way that the three-dimensional datageneration unit 21 generates the three-dimensional data through acoordinate system that is specified by the beam deflection angle ψ_(a)with respect to the reference axis A_(sa) that is perpendicular to thebeam axis X_(B) and passes through the reference point CPa, the beamdeflection angle ψ_(b) with respect to the reference axis A_(sb) that isperpendicular to the beam axis X_(B) and the reference axis A_(sa) andpasses through the reference point CPb, and the distance r from thereference axis A_(sa) or A_(sb), or from the reference point CPa or CPb.As a result, the leaf driving command value for forming the shape of theopening portion in accordance with the shape of a diseased site can begenerated by directly utilizing the three-dimensional data that isinputted to or outputted from the treatment planning apparatus 20. Inother words, in the control data generation unit 23, the control datacan be specified by two deflection angles ψ_(a) and ψ_(b); therefore, ina particle beam therapy system that can suppress a penumbra in anirradiation system in which a particle beam spreads in aseries-of-scanners manner and that can irradiate a high-contrast and anexcellent beam, it is made possible to perform a high-contrast andhigh-accuracy irradiation.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1: wobbler electromagnet        -   1 a: x-direction (upstream) scanning electromagnet        -   1 b: y-direction (downstream) scanning electromagnet    -   2: ridge filter    -   3: range shifter    -   4: ring collimator    -   5: multi-leaf collimator        -   5 _(L): leaf plate        -   5 _(G): leaf group        -   5 _(D): leaf driving unit    -   6: bolus    -   10: particle beam therapy system    -   20: treatment planning apparatus    -   21: three-dimensional data generation unit    -   22: irradiation condition setting unit    -   23: control data generation unit    -   A_(sa): scanning axis (1st axis) of upstream scanning        electromagnet (E_(As): virtual axis)    -   A_(sb): scanning axis (2nd axis) of downstream scanning        electromagnet    -   CPa: 1st reference point    -   CPb: 2nd reference point    -   E_(L): facing end face of leaf plate    -   F_(B): beam bundle (spread) of particle beam    -   OL: driving orbit of leaf plate    -   P_(I): beam-incident-side end face (adjacent to E_(L)) of leaf        plate    -   P_(L): thickness-direction facing side of leaf plate    -   PS: penetration shape    -   P_(x): beam-emission-side end face (adjacent to E_(L)) of leaf        plate    -   ST: scanning locus of particle beam    -   X_(B): beam axis of particle beam        -   (E_(X): beam axis of beam entering multi-leaf collimator)

Three-digit numbers each denote variant examples in Embodiments.

The invention claimed is:
 1. A particle beam therapy system comprising:an irradiation nozzle that scans and irradiates a particle beam suppliedfrom an accelerator, by use of two electromagnets whose scanningdirections are different from each other, said two electromagnetsincluding an upstream electromagnet and a downstream electromagnet; anda multileaf collimator that is disposed on a beam orbit of a particlebeam irradiated from the irradiation nozzle and that limits or forms anirradiation field of the charged particle beam in such a way that theirradiation field conforms to the shape of an irradiation subject, themultileaf collimator comprising: a leaf row in which a plurality of leafplates are arranged in a thickness direction thereof in such a way thatrespective inner end faces of the leaf plates are trued up; and a leafplate drive mechanism configured to (i) drive each of the plurality ofleaf plates in such a way that an inner end face approaches or departsfrom a beam axis of the charged particle beam and (ii) drive theplurality of leaf plates along a circumferential orbit around a scanningaxis of the downstream electromagnet and at a preset distance from thescanning axis of the downstream electromagnet, wherein the particle beamis irradiated through a scanning method.
 2. The particle beam therapysystem according to claim 1, wherein in each of the plurality of leafplates, a facing side facing a leaf plate that is adjacent to that leafplate in the thickness direction is formed of a plane including ascanning axis of the upstream electromagnet, which is perpendicular tothe beam axis and is set at a first position on the beam axis, andwherein the circumferential orbit along the scanning axis of thedownstream electromagnet, around which the plurality of leaf plates aredriven, is perpendicular to the beam axis and the scanning axis of theupstream electromagnet and is set at a second position that is on thebeam axis and separates from the first position by a predetermineddistance.
 3. The particle beam therapy system according to claim 2,wherein the respective inner end faces of the plurality of leaf platesare on a plane including the scanning axis of the downstreamelectromagnet.
 4. The particle beam therapy system according to claim 2,wherein the respective inner end faces of the plurality of leaf platesare driven by the leaf plate drive mechanism in such a way as to be on aplane including the scanning axis of the downstream electromagnet. 5.The particle beam therapy system according to claim 1, wherein each ofthe leaf plates of the plurality of leaf plates has four end faces, andwherein an incident-side end face and an emitting-side end face, amongthe four end faces, which are adjacent to the inner end face, are formedin the shape of an arc whose center is the scanning axis of thedownstream electromagnet.